SIDE EFFECTS: Upset stomach, dizziness, or headache may occur as your body adjusts to the medication. If any of these effects last or get worse, tell your doctor or pharmacist promptly. To reduce the risk of dizziness and lightheadedness, get up slowly when rising from a sitting or lying position. Remember that your doctor has prescribed this medication because he or she has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects. Tell your doctor right away if you have any serious side effects, including: decrease in vision, eye pain. This medication may cause a loss of too much body water (dehydration) and salt/minerals. Tell your doctor right away if you have any symptoms of dehydration or mineral loss, including: extreme thirst, very dry mouth, muscle cramps/weakness, slow/fast/irregular heartbeat, confusion, decreased urination. A very serious allergic reaction to this drug is rare. However, get medical help right away if you notice any symptoms of a serious allergic reaction, including: rash, itching/swelling (especially of the face/tongue/throat), severe dizziness, trouble breathing. This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist. In the US - Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088 or at www.fda.gov/medwatch. In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.

PRECAUTIONS: Before taking hydrochlorothiazide, tell your doctor or pharmacist if you are allergic to it; or if you have any other allergies. This product may contain inactive ingredients (such as sulfites found in some brands), which can cause allergic reactions or other problems. Talk to your pharmacist for more details. Before using this medication, tell your doctor or pharmacist your medical history, especially of: diabetes, gout, kidney disease, liver disease, lupus. This drug may make you dizzy. Alcohol or marijuana can make you more dizzy. Do not drive, use machinery, or do anything that needs alertness until you can do it safely. Limit alcoholic beverages. Talk to your doctor if you are using marijuana. Severe sweating, diarrhea, or vomiting can increase the risk for a serious loss of body water (dehydration). Report prolonged diarrhea or vomiting to your doctor. To prevent dehydration, drink plenty of fluids unless your doctor directs you otherwise. If you have diabetes, hydrochlorothiazide may affect your blood sugar. Check your blood sugar regularly as directed by your doctor. Your doctor may need to adjust your diabetes medication, exercise program, or diet. This drug may decrease your potassium levels. Ask your doctor about foods high in potassium (such as bananas, orange juice) or about using a salt substitute containing potassium. A potassium supplement may be prescribed by your doctor. This medication may make you more sensitive to the sun. Limit your time in the sun. Avoid tanning booths and sunlamps. Use sunscreen and wear protective clothing when outdoors. Tell your doctor right away if you get sunburned or have skin blisters/redness. Before having surgery, tell your doctor or dentist about all the products you use (including prescription drugs, nonprescription drugs, and herbal products). Older adults may be more sensitive to the effects of this drug, especially dizziness. During pregnancy, this medication should be used only when clearly needed. Discuss the risks and benefits with your doctor. This drug passes into breast milk, but is unlikely to harm a nursing infant. Consult your doctor before breast-feeding.

DRUG INTERACTIONS: See also How To Use section. Drug interactions may change how your medications work or increase your risk for serious side effects. This document does not contain all possible drug interactions. Keep a list of all the products you use (including prescription/nonprescription drugs and herbal products) and share it with your doctor and pharmacist. Do not start, stop, or change the dosage of any medicines without your doctor's approval. Some products that may interact with this drug include: dofetilide, lithium. Some products have ingredients that could raise your blood pressure or worsen your swelling. Tell your pharmacist what products you are using, and ask how to use them safely (especially cough-and-cold products, diet aids, or NSAIDs such as ibuprofen/naproxen). This medication may interfere with certain lab tests (such as parathyroid function), possibly causing false test results. Make sure lab personnel and all your doctors know you use this drug.

OVERDOSE: If someone has overdosed and has serious symptoms such as passing out or trouble breathing, call 911. Otherwise, call a poison control center right away. US residents can call their local poison control center at 1-800-222-1222. Canada residents can call a provincial poison control center. Symptoms of overdose may include: severe dizziness, weakness, fainting.